A recent study in Pediatrics suggests that about 1% of US children have autism or a related disorder. That’s nearly 50% higher than previous estimates.

To determine the prevalence of the condition among US children aged 3 to 17 years, Michael Kogan and colleagues at the Health Resources and Services Administration and the CDC queried data from the 2007 National Survey of Children’s Health, which involved outbound calls to more than 78,000 parents.

In the Survey, parents were asked whether a health care provider had ever told them their child had autism, Asperger’s disorder, or pervasive developmental disorder, which are the 3 behavioral conditions that comprise Autism spectrum disorder, or ASD.

Parents who said yes were then asked whether their child had the condition at the time of the call.

The scientists found that 673,000 children had ASD, which equates to a prevalence just above 1%. The odds of having ASD were 4 times higher in boys than in girls. Non-Hispanic black and multiracial children had lower odds of ASD than white children.

Interestingly, parents reported that 40% of all children who were once labeled as having ASD did not currently have it, a finding that suggests over-diagnosis of the condition since there is no known cure.

The reported 1% prevalence is higher than that cited by the previous gold-standard study on the subject, which was published in 2003. It said the prevalence was 1 in 150.

But many urged caution about the apparent change in prevalence. “We don’t know whether the change over time is a result of the change in the actual condition or due to the fact that the condition is being recognized differently,” the CDC’s Ileana Arias told CNN.

The study raises “a lot of questions about how we are preparing in terms of housing, employment, social support — all the issues that many of these people are going to need,” added Tom Insel, who directs the National Institute of Mental Health.